In recent years, HDMI® has been in widespread use as a high-speed communication interface for transmitting at high speed a digital television signal, i.e., pixel data of uncompressed (baseband) images and audio data associated with the images, for example, from a digital versatile disc (DVD) recorder, a set-top box, or other audio visual (AV) sources to a television set, a projector, or other displays.
The HDMI specification defines Transition Minimized Differential Signaling (TMDS) channel for high speed unidirectional transmission of pixel data and audio data from an HDMI® source to an HDMI® sink and Consumer Electronics Control line (CEC line) for bidirectional communication between an HDMI® source and an HDMI® sink, and the like.
For example, as shown in FIG. 1, pixel data and audio data can be transmitted at high speed by connecting a digital television set 11 to an AV amplifier 12 using an HDMI® cable 13 that complies with the HDMI® specification.
The digital television set 11 and AV amplifier 12 and a reproducing apparatus 14 are placed in a living room of a user house. In FIG. 1, the living room is located on the left side. The digital television set 11 is connected to the AV amplifier 12 using the HDMI® cable 13. The AV amplifier 12 is connected to the reproducing apparatus 14 using an HDMI® cable 15.
In addition, a hub 16 is placed in the living room. The digital television set 11 and reproducing apparatus 14 are connected to the hub 16 using local area network (LAN) cables 17 and 18, respectively. In a bedroom located to the right of the living room in the drawing, a digital television set 19 is placed. The digital television set 19 is connected to the hub 16 via a LAN cable 20.
For example, when content recorded in the reproducing apparatus 14 is played back and an image is displaying on the digital television set 11, the reproducing apparatus 14 decodes pixel data and audio data serving as the playback content. Thereafter, the reproducing apparatus 14 supplies the decoded uncompressed pixel data and audio data to the digital television set 11 via the HDMI® cable 15, the AV amplifier 12, and the HDMI® cable 13. On the basis of the pixel data and audio data supplied from the reproducing apparatus 14, the digital television set 11 displays images and outputs sounds.
When content recorded in the reproducing apparatus 14 is played back and images are displayed on the digital television sets 11 and 19 at the same time, the reproducing apparatus 14 supplies compressed pixel data and audio data serving as the content to be played back to the digital television set 11 via the LAN cable 18, the hub 16, and the LAN cable 17. In addition, the reproducing apparatus 14 supplies the compressed pixel data and audio data to the digital television set 19 via the LAN cable 18, the hub 16, and the LAN cable 20.
The digital television sets 11 and 19 decode the pixel data and audio data supplied from the reproducing apparatus 14, display images, and output sounds on the basis of the decoded uncompressed pixel data and audio data.
When the digital television set 11 receives pixel data and audio data for playing back a program over television broadcasting and if the received audio data is audio data of, for example, 5.1-channel surround sounds which the digital television set 11 is unable to decode, the digital television set 11 converts the audio data into an optical signal and transmits the optical signal to the AV amplifier 12.
Upon receiving the optical signal transmitted from the digital television set 11, the AV amplifier 12 photoelectrically converts the optical signal into audio data. Thereafter, the AV amplifier 12 decodes the converted audio data. Subsequently, the AV amplifier 12 amplifies the decoded uncompressed audio data when necessary so as to output sounds from surround speakers connected thereto. In this manner, the digital television set 11 can play back a 5.1-channel surround television program by decoding the received pixel data and displaying images by using the decoded pixel data and by outputting sounds from the AV amplifier 12 in accordance with the audio data supplied to the AV amplifier 12.
In addition, an HDMI®-based apparatus has been proposed in which, when pixel data and audio data are transmitted from an HDMI® source to an HDMI® sink, unnecessary data is muted by turning on/off the data transmission (refer to, for example, Patent Document 1).
Furthermore, an HDMI®-based apparatus has been proposed in which, by using a selector switch and selecting a terminal from which the pixel data and audio data are output, an HDMI® source can output pixel data and audio data to a desired HDMI® sink among a plurality of HDMI® sinks without changing cable connection between the HDMI® source and the HDMI® sink (refer to, for example, Patent Document 2).    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-57714    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2006-19948